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PerceptionPerceptionChapter 6Chapter 6

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Perception

Selective Attention

Perceptual Illusions

Perceptual Organization Form Perception Motion Perception Perceptual Constancy

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Perception

Perceptual Interpretation Sensory Deprivation and

Restored Vision Perceptual Adaptation Perceptual Set Perception and Human Factor

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Perception

The process of selecting, organizing, andinterpreting sensory information, which enables us

to recognize meaningful objects and events.

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Selective AttentionPerceptions about objects change from moment to

moment. We can perceive different forms of theNecker cube; however, we can only pay attention

to one aspect of the object at a time.

Necker Cube6

Example: Cocktail Party Effect

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Inattentional Blindness

Inattentional blindness refers to the inabilityto see an object or a person in our midst.

Simmons & Chabris (1999) showed that halfof the observers failed to see the gorilla-suited assistant in a ball passing game.

Dan

iel S

imon

s, U

nive

rsity

of I

llino

is

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Change Blindness

Change blindness is a form of inattentionalblindness in which two-thirds of individuals

giving directions failed to notice a change in theindividual asking for directions.

© 1998 Psychonomic Society Inc. Image provided courtesy of Daniel J. Simmons.

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Change Blindness Video

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Perceptual Illusions

Illusions provide good examples inunderstanding how perception is organized.Studying faulty perception is as important as

studying other perceptual phenomena.

Which line is longer?

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Tall Arch

In this picture, thevertical dimensionof the arch lookslonger than the

horizontaldimension.

However, both areequal.

Rick Friedman/ Black Star

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Illusion of a Worm

The figure on the right gives the illusion of a blue hazy“worm” when it is nothing else but blue lines identical

to the figure on the left.

© 1981, by perm

ission of Christoph R

edies and Lothar Spillm

ann and Pion Limited, London

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3-D Illusion

It takes a great deal of effort to perceive this figure intwo dimensions.

Reprinted w

ith kind permission of Elsevier Science-N

L. Adapted from

H

offman, D

. & R

ichards, W. Parts of recognition. C

ognition, 63, 29-78

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Escher Drawing

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Organization of the visual field into objects(figures) that stand out from their surroundings

(ground).

Form Perception

Time Savings Suggestion, ©

2003 Roger Sheperd.

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Perceptual Organization

When vision competes with our othersenses, vision usually wins – a phenomena

called visual capture.

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Visual Capture Examplee.g., movie projector voices (vision overtakes hearing)

This can be true with other senses as welle.g., finger touch and various tones; feeling like we’re moving when

simply watching an action movie18

Sensory and Perception BlendHow do we form meaningful perceptions from

sensory information?

We organize it!Gestalt psychologists showed that a figure formed

a “whole” different than its surroundings.

Our brains do a heck of a lot more than just merelyregister information about the world!

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Gestalt Psychologists: Grouping

After distinguishing the figure from the ground,our perception needs to organize the figure into

a meaningful form using grouping rules.

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Grouping & Reality

Although grouping principles usually help us constructreality, they may occasionally lead us astray.

Both photos by W

alter Wick. R

eprinted from G

AM

ES M

agazine. .© 1983 PC

S Gam

es Limited Partnership

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Patterns

• Naturally we look forpatterns in life

• In addition to visualpatterns, we alsoconcoct patterns withour other senses

e.g., We tend to hear clock’s go“tick TICK tick TICK”, but inreality, the sounds are thesame-“tick tick tick tick”,

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Depth Perception

Visual Cliff

Depth perception enables us to judge distances.Gibson and Walk (1960) suggested that human

infants (crawling age) have depth perception. Evennewborn animals show depth perception.

Inne

rvisi

ons

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Binocular Cues:Need the use of two eyes

Retinal disparity: Images from the two eyes differ. Trylooking at your two index fingers when pointing them

towards each other half an inch apart and about 5 inchesdirectly in front of your eyes. You will see a “finger

sausage” as shown in the inset.

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Binocular Cues

Convergence: Neuromuscular cues. When two eyes moveinward (towards the nose) to see near objects and outward

(away from the nose) to see faraway objects.*Two eyes are better than one!

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Monocular Cues:Can use eyes together or either eye alone

Relative Size: If two objects are similar in size, weperceive the one that casts a smaller retinal image

to be farther away.

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Monocular Cues

Interposition: Objects that occlude (block) otherobjects tend to be perceived as closer.

Rene M

agritte, The Blank Signature, oil on canvas, N

ational Gallery of A

rt, Washington. C

ollection of M

r. and Mrs. Paul M

ellon. Photo by Richard C

arafelli.

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Monocular Cues

Relative Clarity: Because light from distant objectspasses through more light than closer objects, we

perceive hazy objects to be farther away thanthose objects that appear sharp and clear.

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Monocular Cues

Texture Gradient: Indistinct (fine) texture signalsan increasing distance.

© Eric Lessing/ A

rt Resource, N

Y

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Monocular Cues

Relative Height: We perceive objects that are higher in ourfield of vision to be farther away than those that are lower.

Image courtesy of Shaun P. V

ecera, Ph. D.,

adapted from stim

uli that appered in Vecrera et al., 2002

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Monocular Cues

Relative motion: Objects closer to a fixation point movefaster and in opposing direction to those objects that are

farther away from a fixation point, moving slower and inthe same direction. This is how we compute objects’

distances.

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Monocular Cues

Linear Perspective: Parallel lines, such as railroadtracks, appear to converge in the distance. The

more the lines converge, the greater theirperceived distance.

© The N

ew Y

orker Collection, 2002, Jack Ziegler from

cartoonbank.com. A

ll rights reserved.

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Monocular Cues

Light and Shadow: Nearby objects reflect more light intoour eyes than more distant objects. Given two identical

objects, the dimmer one appears to be farther away.

From “Perceiving Shape From

Shading” by Vilayaur

S. Ram

achandran. © 1988 by Scientific A

merican, Inc.

All rights reserved.

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Motion PerceptionMotion Perception: Objects traveling towards usgrow in size and those moving away shrink in

size. The same is true when the observer moves toor from an object.

e.g., driving

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Apparent Motion

Phi Phenomenon: When lights flash at a certainspeed they tend to present illusions of motion.Neon signs use this principle to create motion

perception.

Two lights flashing one after the other.One light jumping from one point to another: Illusion of motion.

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Perceptual Constancy

Perceiving objects as unchanging even asillumination and retinal images change. Perceptualconstancies include constancies of shape and size.

Shape Constancy 36

Size Constancy

Stable size perception amid changing size of thestimuli.

Size Constancy

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Size-Distance Relationship

The distant monster (below, left) and the top redbar (below, right) appear bigger because of

distance cues.

From Shepard, 1990

Alan C

hoisnet/ The Image B

ank

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Size-Distance Relationship

Both girls in the room are of similar height.However, we perceive them to be of differentheights as they stand in the two corners of the

room.

Both photos from S. Schwartzenberg/ The Exploratorium

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Ames Room

The Ames room is designed to demonstrate the size-distance illusion.

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Lightness Constancy

The color and brightness of square A and B are the same.Cou

rtesy

Edw

ard A

delso

n

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Perceiving familiar objects as having consistentcolor even when changing illumination filters

the light reflected by the object.

Color Constancy

Color Constancy 42

Visual Illusions Video

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Perceptual Interpretation

Immanuel Kant (1724-1804) maintained thatknowledge comes from our inborn ways of

organizing sensory experiences.

John Locke (1632-1704) argued that we learn toperceive the world through our experiences.

How important is experience in shaping ourperceptual interpretation?

e.g., Amadou Diallo and police incident

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Video Time

What happens when we have sensationwithout perception?

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Restored Vision

After cataract surgery,blind adults were ableto regain sight. These

individuals coulddifferentiate figure andground relationships,yet they had difficultydistinguishing a circle

and a triangle(Von Senden, 1932).

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Facial Recognition

After blind adultsregained sight, they wereable to recognize distinctfeatures, but were unable

to recognize faces.Normal observers alsoshow difficulty in facial

recognition when thelower half of the pictures

are changed.

Courtesy of R

ichard LeGrand

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Kittens raisedwithout exposure tohorizontal lines later

had difficultyperceiving horizontal

bars.

Blakemore & Cooper (1970)

Sensory Deprivation

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Perceptual Adaptation

Visual ability to adjustto an artificially

displaced visual field,e.g., prism glasses.

Courtesy of Hubert D

olezal

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Perceptual Set

A mental predisposition to perceive one thingand not another. What you see in the centerpicture is influenced by flanking pictures.

From Shepard, 1990.

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(a) Loch ness monster or a tree trunk;(b) Flying saucers or clouds?

Perceptual Set

Other examples of perceptual set.

Frank Searle, photo Adam

s/ Corbis-Sygm

a

Dick R

uhl

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Children's schemas represent reality as well as theirabilities to represent what they see.

SchemasSchemas are concepts that organize and

interpret unfamiliar information.Schemas develop through experience.

Courtesy of Anna Elizabeth V

oskuil

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Students recognized a caricature of ArnoldSchwarzenegger faster than his actual photo.

Features on a Face

Face schemas are accentuated by specificfeatures on the face.

Kieran Lee/ FaceLab, D

epartment of Psychology,

University of W

estern Australia

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Eye & Mouth

Eyes and mouth play a dominant role in facerecognition.

Courtesy of C

hristopher Tyler

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Is the “magician cabinet” on the floor or hanging from theceiling?

Context Effects

Context can radically alter perception.

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To an East African, the woman sitting is balancing a metalbox on her head, while the family is sitting under a tree.

Cultural Context

Context instilled by culture also altersperception.

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Perception Revisited

Is perception innate or acquired?

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Perception & Human Factors

Human Factor Psychologists design machines thatassist our natural perceptions.

The knobs for the stove burners on the right are easier tounderstand than those on the left.

Photodisc/ P

unchstock

Courtesy of G

eneral Electric

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Human Factors & Misperceptions

Understanding human factors enables us todesign equipment to prevent disasters.

Two-thirds of airline crashes caused by human error arelargely due to errors of perception.

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Human Factors in Space

To combat conditions of monotony, stress, andweightlessness when traveling to Mars, NASA

engages Human Factor Psychologists.

Transit Habituation (Transhab), NASA 60

Is There Extrasensory Perception?

Perception without sensory input is calledextrasensory perception (ESP). A large percentage

of scientists do not believe in ESP.

Claims of ESP Premonitions or Pretensions Putting ESP to Experimental Test

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Claims of ESPParanormal phenomena include astrological

predictions, psychic healing, communication withthe dead, and out-of-body experiences, but most

relevant are telepathy, clairvoyance, andprecognition.

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Claims of ESP

Telepathy: Mind-to-mind communication. Oneperson sending thoughts and the otherreceiving them.

Clairvoyance: Perception of remote events,such as sensing a friend’s house on fire.

Precognition: Perceiving future events, such asa political leader’s death.

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Putting ESP to Experimental Test

In an experiment with 28,000 individuals,Wiseman attempted to prove whether or not onecan psychically influence or predict a coin toss.

People were able to correctly influence or predicta coin toss 49.8% of the time.

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Premonitions or Pretensions?Can psychics see the future?

Can psychics aid police inidentifying locations of

dead bodies? What aboutpsychic predictions of the

famous Nostradamus?

The answers to thesequestions are NO!

Nostradamus’ predictionsare “retrofitted” to events

that took place after hispredictions.

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Review SessionReview Sessionfor Exam 2for Exam 2

Wednesday, Feb 13Wednesday, Feb 13thth

5:30-6:30pm5:30-6:30pmLocation: In this roomLocation: In this room

Bring Questions!Bring Questions!